Conventionally, image data supplied to an image display device is often subjected to various image processing steps before supplied to a display section, to improve the quality of the image displayed in the display section. The image processing steps as above are such as an image processing concerned with overshoot drive, white balance correction, color correction and so forth.
The overshoot drive is a driving method for improving the speed of the response of a culminatively responding liquid crystal panel. In the image processing concerned with the overshoot drive, a gradation value of the image data of the current field and that of the previous field are compared, and in accordance with the result thereof, a voltage applied to a liquid crystal pixel in the current field, i.e. the density of the image data of the current field is converted. In other words, the image processing concerned with the overshoot drive includes the comparison of the sets of image data of time series continuous fields.
The white balance correction is a step of the image processing in which sets of gradation data, R (red), G (green), and B (blue) are respectively adjusted in accordance with the transmittance of the liquid crystal panel. That is to say, in the liquid crystal panel, the balance of RGB luminance is lost due to wavelength dispersion when transmittance of the pixel is altered, and hence it is necessary to recover the balance by dint of the white balance correction. Moreover, since a color liquid crystal panel is arranged such that a single color pixel includes sub-pixels aligned therein and respectively matched with R, G, and B, the gradation values of these sub-pixels have to be compared with each other in the white balance correction. In other words, the white balance correction includes the data comparison of the spatially continuous sets of the data of pixels.
The color correction is a step of the image processing for avoiding a color, which is not supposed to be supplied, being displayed due to characteristics of the image display device. In the color correction, R, G, and B signals of each pixel are adjusted without disturbing white balance so as to be transmitted. In this step, it is again necessary to compare the gradation values between the aligned sub-pixels respectively matched with R, G, and B, and the data comparison between the spatially continuous pixels is also included. Moreover, the color correction may include the time series data comparison.
As illustrated above, the image processing includes the step which requires to subject the supplied image data to time series or spatial data comparison, and an image processing circuit which conducts the processing in time series manner is, for instance, arranged as illustrated in FIG. 16.
The image processing circuit as illustrated in FIG. 16 is arranged such that a set of supplied image data is split into two or more parts (two in the figure) and one part is directly supplied to an image processing section 101 whereas the other part is temporarily stored in a memory 102 and then supplied to the image processing section 101 after one field delay.
That is, in the above-mentioned image processing circuit, the part of the image data directly supplied to the image processing section 101 indicates the current field, meanwhile the part of image data supplied to the image processing section 101 via the memory 102 indicates the previous field. The image processing section 101 compares the supplied image data of the current field with that of the previous field, and as a result of this, the image data of the current field is converted so as to be supplied to a display section.
In the meantime, as image data to be supplied in the image display device, interlace image data (hereinafter, will be referred to as interlace signals) may be supplied. The interlace signals are arranged such that, as FIG. 17 shows, in each field image, signals containing data are supplied in every other scanning line, and moreover, a line containing data in the current field is vertically shifted to a next line in the subsequent field or the previous field.
However, when the above-identified image processing, which requires the time series data comparison, is conducted in the image processing circuit to which the interlace signals are supplied, as FIG. 17 illustrates, lines in two consecutive fields (previous field and current field), which respectively contain a set of image data to be compared, are mismatched.
That is to say, to compare signals in a line N of the current field with signals of the previous field, basically the target of comparison should be signals in a line N of the previous field. However, the interlace signals are arranged such that a line containing data in a field vertically shifts to the next line in the consecutive field so that when data exists in the line N of the current field, there is no data in the line N of the previous field.
Thus in the image processing circuit to which the interlace signals are supplied, it is impossible to compare the sets of the data in the same lines, so that the data comparison is conducted between (a) a line and (b) another line which is immediately above or below the line to be compared. As a result, this could cause significant degradation of the quality of the image and in some cases a breakdown of the image processing.
Moreover, in the case of spatial data comparison in the image processing circuit, image processing devices of late are required to produce vivid and high-definition image so that it has been attempted to exploit the full potential of the device.
A device such as CRT (Cathode-Ray Tube), which is high-contrast and does not involve the change of the color in accordance with the gradation, can obtain the image with higher definition by improving the signal precision (for instance, to 8 bit). In the meantime, a device such as LCD (Liquid Crystal Display) which has relatively poor color reproductivity could lose the balance of whole image, when color of a pixel is modified without considering harmony with surrounding pixels.
Thus, to avoid this happens, it is necessary to modify the image in consideration with the balance by comparing colors between neighboring pixels (including pixels on neighboring scanning lines), in the image processing including the spatial data comparison such as the white balance correction and the color correction.
However, in this case, when the image data supplied to the image processing device is interlace signals, the data comparison between the neighboring lines could have a problem such that a part of the image data to be compared does not exist in the same field, and hence the precision of the image processing could be deteriorated.